JPS6281535A - Circuit device for shortening rise time of logarithmic amplifier connected to photoelectric element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit device for shortening the start-up time of a logarithmic amplifier whose input is the output of a photoelectric element.

[Conventional technology]

For photodiode output currents, logarithmic amplifiers generally exhibit switching problems when their photodiode output currents are very small.

That is, the start-up transient that occurs during switching is related to the rectifying characteristics of the logarithmic diode to which the amplifier is connected, so that all voltage spikes of one polarity enter the photodiode, whereas for the other polarity, A logarithmic diode works to completely block that spike. As a result, the photodiode charges in the wrong direction. The discharge can be caused by a very small photocurrent since the photodiode and logarithmic diode are at very high voltage. In most cases, the photodiode probably has a large capacity, so this discharge requires a long time which is in any case a nuisance. Because of this mischarging, the output of the amplifier is fixed at a constant but undesirable value for a period of time after switching. Therefore, the circuit does not amplify the sensing current corresponding to the small amount of light and does not operate normally until the erroneously charged charge of the photoelectric element is removed.

In order to shorten this so-called switching time, DE 2833217 proposes to lead the input of an amplifier connected to the photoelectric element to an auxiliary voltage via a differential circuit.

However, this circuit device must satisfy strict conditions regarding residual current, which makes it technically expensive and poses a problem in terms of stability. Furthermore, correct instruction immediately after application of the operating voltage is not possible.

In order to simplify the construction of a circuit arrangement in which a differential amplifier is connected to a photodiode, the output of which is fed back via a logarithmic diode to its inverting input, it is used as an input stage for an exposure control circuit of a photographic camera. German Publication No. 3113
No. 220 proposes to "reduce" the positive feedback current flowing through the logarithmic diode in the rising transient phase of the input stage.

This is because, despite the reduction of the positive feedback current flowing through the logarithmic diode, a rising phase occurs during switching at the operating point, which is also the cause of the problem of false charging, so that the exposed control circuit immediately after application of the operating voltage to the circuit device. The disadvantage is that information cannot be extracted from the

[Problem that the invention seeks to solve]

In order to reduce the start-up time of the amplifier connected to the photoelectric element, the structure of the circuit device becomes complicated, the operation becomes unstable, and the occurrence of erroneous charging immediately after application of the operating voltage and the inability to receive instructions are required. There is a problem.

[Means for solving problems]

According to the invention, in a circuit arrangement for shortening the rise time of a logarithmic amplifier connected to a photoelectric element, a control of a simple construction prevents incorrect charging of components by applying an operating voltage to their components. The above problems are solved by means.

[For production]

This control means eliminates erroneous charging of the photoelectric element and puts the de-energized exposure control circuit in a condition to give error-free and immediately displayable measurements immediately after switching the operating voltage. That is, when applying the operating voltage of this circuit device, it cooperates with the components of this circuit device to prevent erroneous charging of the photoelectric element, and in the meantime, it gives the amplifier a long time to reach its operating point, and prevents a steep rise. interfere with

In other embodiments, this control means acts to prevent erroneous charging due to switching by immediately directing it to other parts.

〔Example〕

In the embodiment of FIG. 1 showing a circuit arrangement with an operational amplifier OP2 acting on a current-voltage converter and a nonlinear element (logarithmic diode) D+ converting the current derived from the background luminance into a logarithmic voltage, the switch l is A power supply connects to the circuit device via. Accordingly, the transistors T and T2, connected as diodes, are at the supply voltage, so that each transistor is supplied with a different current through Rs'(f') to the resistor.The differential voltage caused by these currents is , an operational amplifier OP having a positive feedback path including a resistor R12.

The output of the amplifier OB is connected at one pole to a temperature compensating diode, and the other pole to the diode is connected to a resistor RI2 and variable resistors P, , P2 . Connect to R8v, 几, .

Nonlinear element D1 and variable resistors P, , P2. R3
The sliders v, R, TV are connected to at least one operational amplifier stage OP3 via resistors RI7--. Amplification stage O
P is the emitter of the switch transistor T6 and the resistor R
A resistor R2□ is connected between 17 and the common connection point of I(?,
has.

Furthermore, another similar system (OF2, Rs+ to R34°R27) is provided.

When using high-sensitivity film, the exposure time must be set accordingly, even when the background brightness is very low, i.e., the photodiode 18 must be in the pure amperage range and can be processed reliably in practice. It can produce a current that is not high. Therefore, errors may occur in measuring the background brightness, resulting in erroneous photography.

To avoid this, the inverting input of the comparator OP6 is connected to the output of the amplifier OP2, which acts on the current-to-voltage converter.
As a result, the light emitting diodes LED and LED 'i, which are read directly from the outputs of the operational amplifiers OP and OF2, are turned off when the luminance is below the limit luminance of the object to be measured.

At the non-inverting input of the comparator OP6, in this embodiment a photodiode LED is selected, independent of the room temperature, when n is above or below a value previously set in the exposure meter for the limit illuminance.
, is contacted and read by the potentiometer pao which creates a guideline for the indication limit of the exposure meter, which is LED2.

The output of comparator OP6 is connected to the pace of transistor T8 via resistor R3□. When this output goes to a positive potential, transistor T8 shuts off and therefore the diode LED,
Then, current no longer flows to LED2.

From the temperature dependence of a diode, it is clear that the higher the temperature, the greater the reverse current flowing through it. With this circuit arrangement, large fault currents will flow at the input of the operational amplifier. The same applies to the reverse current of the photodiode 3. Therefore, the operational amplifier OP2 also generates a large erroneous current at room temperature (22° C.), for example. According to this circuit device, for example, at +60° C., the preset value for the limit illuminance (at which point the instruction is stopped) may be twice as high.

When the operating voltage is applied to the circuit device, a transient oscillation occurs in the operational amplifier OP2, and its output becomes a +” supply potential for a short time. At that time, the capacitance of the photodiode D3 is discharged through the nonlinear element D1. to generate a positive charge at the inverting input of the operational amplifier OP2.The inverting input of the operational amplifier OP20, the photodiode D3, and the nonlinear element D1 are
At this time, since there is a large ohmic connection in the opposite direction, this charge is not automatically discharged.

The output of the operational amplifier OP2 is then at a very low potential, so that the comparator OP6 is connected to the photodiode LED1.
and turns off the display by LED2. However, in the lower limit illuminance region, the photocurrent required to recharge the photodiode D is small, so the display is turned off. This temporal "pause" is caused by resistor R6□, diode D3, resistor R1, and resistor R1 connected to the output of operational amplifier OP2.
41 and a capacitor Cl42, and when the operating voltage is applied, the logarithmic diode D1 is oscillatedly prevented from reaching a positive potential by the capacitor C742 via the diode D3 and the resistor RI46. Since this occurs gradually due to its damping characteristics, operational amplifier OP2 has an oscillation time as shown in FIG. In this figure, the anode to the logarithmic diode acts to absorb the voltage spike that would otherwise occur in time.

In the embodiment shown in FIG. 2, in addition to the resistor R shown in FIG. 1, a circuit section 5 consisting of an inverse diode D8o and a grounded capacitor C connected in series thereto is provided at the output of the operational amplifier OP. A resistor R8o that receives the operating voltage is connected between the diode D8° and the capacitor C8o.

Via the resistive island 7, the diode D9 and the capacitor C8°, the voltage spike at the output of the operational amplifier OP2 when the operating voltage is applied is short-circuited. Charging of capacitor C8o by the operating voltage then occurs via resistor R8o. As a result, the diodes D&, are turned off, and the operational amplifier O, which has a positive feedback path consisting of the logarithmic diode and the capacitor C2,
P2 can now operate normally as a logarithm part. According to the present invention, an appropriate period of time to reach the operating point can be obtained in proportion to the operating time of the operational amplifier.

In the variant shown in FIG. 3, the voltage spike that occurs at the output of the operational amplifier OP2 due to the application of the operating voltage is removed without being caused by a short circuit. This consists of diode D81, resistor R81, capacitor C8□, and the resistance between them and the operating power supply.
%2 and flows through circuit section 6 which is connected in parallel with photodiode D3 to the inverting input of operational amplifier OP2.

The erroneous charge that is superimposed on the photodiode D3 when the operating voltage is applied is guided through the diode D81, the resistor R6, and the capacitor Cart.
If 81 is charged to the operating voltage through resistor R82k, diode D8□ will not have a reverse voltage, and operational amplifier OP
2 can begin its function as a logarithm part by connecting diode D1 and capacitor C2.

In the embodiment shown in FIG. 4, a resistor R84, a capacitor C82,
Voltage section 7 consisting of resistor R84 guides the erroneously charged charge of photodiode D3. This section 7 is connected in parallel with the photodiode D3 and to the non-inverting input of the operational amplifier OP2.

The charge generated by the switch spike is now connected to the resistor R
84 and capacitor C. Then capacitor C8
When □ is discharged through the resistor R8sk and the same potential is applied to the non-inverting input of the operational amplifier OB, no disturbance current flows through the resistor l1 (84) as long as the inverting input of the operational amplifier is at the same potential.

The circuit section 8 used to derive the erroneous charge of the photodiode D3 is shown in FIG. Consisting of
Its control electrode includes a grounded capacitor C91 and a resistor R9.
I is connected.

The interfering charge is extracted through FET T91 k. This discharging phase ends after a constant time determined by the resistor R01 and the capacitor COt (the charging time of the capacitor C91 via the operating voltage). FETT
o is turned off after the end of this discharge phase, so that only the current corresponding to the amount of incident light generated from the photodiode enters the operational amplifier OP2.

As another circuit example for the derivation of the erroneously charged charge of the photodiode D3, FIG. FET T. 1 and the comparator. Consists of 1.

FET T. The control electrode of , is a comparator. , whose drain is grounded and whose source is the operational amplifier 0P.
Connect to 20 inverting input.

To the comparator, the inputs of oI are connected respectively to the output of operational amplifier OP2 and its non-inverting input.

The interfering charge in the circuit arrangement causes the output of the operational amplifier OP2 to be at a low potential, such as its non-inverting input.

, is set, FET T91, C91, K101
, T101.

Furthermore, the amplifier circuit 11 for amplifying the input current of a positive feedback operational amplifier, as in DE 33 21 503, which is driven by a photodiode IO, has a starting problem. If the device is used, for example, with Flashmatic (which measures the illuminance during the flash and automatically shuts off the flash when there is sufficient illumination), the operating voltage is applied to the circuit device before the flash is released. After that, the problem is that there is no light available to drive the photodiode 10 and conduct the current, so the amplifier 11 has not reached its operating point at that time.

Flashes that are at most milliseconds in duration are sufficiently and correctly measured by the process. That is, here too, the amplifier circuit functions without errors by means of suitable electrical control means.

FIG. 7 shows an embodiment of such a processing circuit.

A photodiode 10 between the inputs of the amplifier 11 is associated with a light emitting diode D, . The photodiode 10 includes a switch S, 1. when applying an operating voltage to this circuit device. , which causes a current pulse to be generated from the series circuit consisting of resistor R0 and capacitor CI1+. This light pulse brings the amplifier 11 into its operating range so that the electrical signals generated by the immediately following flash can be processed without error.

A similar configuration is shown in FIG. Again, capacitor CI
Switch S1□ from I circuit consisting of 2□ and resistor R12□
, a current pulse occurs, whereby the light-emitting diode D1□1 following this I-circuit generates a light pulse. This light pulse is converted into a voltage by a photodiode D122 parallel to the photodiode 10, which brings the amplifier 11 into its operating range via the photodiode 10. The difference from the circuit device shown in FIG. 7 is that the light emitting diode D1□1 and the photodiode D1□2 form one optical coupler.

In order to bring the amplifier into its operating range, in the embodiment of FIG. 9 a current pulse is applied to the conductor 12 connected to the anode of the photodiode 10. In the embodiment of FIG. This current pulse is applied to the capacitor C□3. by the closing of the switch S1,1. and resistance R1
3□ and high reverse voltage diode D, 3,
The light is guided to the light emitting element 12 via the light emitting element 12.

Capacitor CI3□ has its series resistance RI31'ff:
, if it is discharged to the ground potential through the amplifier circuit 12
(meaning the end of the rising time), diode D13□
is blocked.

Finally, the circuit of FIG. 10 is also possible. With the illustrated amplifier, the voltage spike caused by switching operational amplifier 14 across switch 13 blocks the photodiode 150 input, thereby causing the non-inverting input of amplifier 14 to move away from its operating point. Due to this, currents generated by narrow light pulses, such as flash lights, are not amplified.

To eliminate this drawback, the two-part capacitor 18
and 19, diodes 20 and 21 and hin...
- An amplifier section consisting of 22n is added to the parallel resistors 23 and 24. This discharges the potential at the non-inverting input of amplifier 14 to ground potential before the operating point is reached. Therefore, amplifier 14
Since both human forces are at the same timing, the potential is the operating range.

This discharge is connected to the FET connected to the junction of portions 16 and 17.
This occurs rapidly as long as 25 is conductive.

During flashing this does not conduct and therefore photodiode 1
The drive according to No. 5 can correctly process the voltage applied by flash light.

Resistors 26, 27, and 28 are connected to the connection point between portions 16 and 17 and in front of elements 18-24, respectively. These act as protective resistors that gradually weaken disturbances reaching the conductor between the amplifier output A and the following capacitor. Furthermore,
This prevents overshoot of amplifier 14 when the switch is closed.

〔Effect of the invention〕

According to the present invention, by using a simple circuit configuration, the rise time of a logarithmic amplifier that receives the output of a photoelectric element as an input is shortened.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment in which the circuit device according to the present invention is applied to an exposure measurement circuit, FIG. 2, FIG. 3, FIG. 4, FIG.
6, 7, 8, 9 and 10 are diagrams showing other embodiments of the present invention, respectively, and FIG. 11 is a diagram showing temporal changes in the anode of a logarithmic diode. be. OP, , OP... operational amplifier op6. , op.
,...Comparator,...Nonlinear (logarithmic) diode 2
Ri...Resistor Ci...Capacitor D2
...Temperature compensation diodes Pl, P2. Rsv, RTv...variable resistance P8o...
・Potentiometer

Claims (13)

[Claims] (1) When applying an operating voltage to the circuit device, the photoelectric element (1
8, D_3) control means (D_3, R
_1_4_0, R_1_4_1, C_1_4_0, D_
8_0, R_8_0, C_8_0) for reducing the rise time of a logarithmic amplifier connected to a photoelectric element. (2) After applying the operating voltage to the circuit device, the photoelectric elements (D_3,
10) control means (D_8, R_8_
2, R_8_2', C_8_1, R_8_3, C_8_
2, T_9_1, C_9_1, R_9_1, K_1_0
_1, T_1_0_1) for reducing the rise time of a logarithmic amplifier connected to a photoelectric element. (3) The control means (D_3, R_4_0, R_1_4
_1, C_1_4_0, D_8_0, R_8_0, C_
8_0) is connected in parallel to the output of the amplifier (OP_2), and its output is gradually released in proportion to the switching time only immediately before the operating point of this amplifier is reached. The circuit arrangement described. (4) The control means (D_8, R_8_2, R_8_2
', C_8_1, R_8_3, R_8_4, C_8_2
, T_9_1, C_9_1, R_9_1, K_1_0_
1, T_1_0_1) is the amplifier (OP_2, 11)
3. The circuit device according to claim 2, wherein the circuit device is connected to an inverting input of the circuit device. (5) The control means (R, R_2) is a logarithmic diode (
3. The circuit device according to claim 2, wherein the circuit device is connected in parallel with D_1, D_2). (6) The control means (D_8, R_8_2, R_8_2
', C_8_1, R_8_3, R_8_4, C_8_2
, T_9_1, C_9_1, K_1_0_1, T_1_
3. The circuit device according to claim 2, wherein the photoelectric element (D_3, 10) is arranged before the photoelectric element (D_3, 10). (7) The circuit device according to claim 2, wherein the control means is a short circuit (T_9_1). (8) Electronic switch (T_9_1) as the control means
8. The circuit device according to claim 7, wherein the circuit device uses: (9) The control means includes photoelectric elements (D_1_1_1, D_
1_2_1) The circuit device according to claim 2. (10) The photoelectric element is an optical coupler (D_1_2_1, D
_1_2_2) The circuit device according to claim 9. (11) A high blocking diode (D_8
) is the resistor (R_8_2') and the RC circuit (R_8_2, C
_8_1) The circuit device according to claim 6, characterized in that it is used in combination with _8_1). (12) The circuit device according to claim 5, characterized in that a resistor is connected in parallel to the logarithmic diode, and its value is proportional to the number of parallel diodes in the bidirectional branch. 13. Circuit arrangement according to claim 5, characterized in that protective resistors (26, 27, 28) are provided for gradually weakening disturbances in order to avoid overshoots.